Cutaneous pathology in onchocerciasis associated with pronounced systemic T-helper 2-type responses to Onchocerca...

Of 18 million people world-wide who are infested with the tissue nematode Onchocerca volvulus, more than 30% are considered to have skin lesions, the pathomechanisms of which are poorly understood.

To relate skin changes associated with onchocerciasis to parasitological findings and systemic cellular immune responses.

In the course of a genetic study, 691 members of 241 families exposed to hyperendemic O. volvulus transmission and free of other filarial or schistosomal infestations were studied clinically, by counting palpable Onchocerca nodules and skin microfilariae, by measuring peripheral blood cell (PBC) counts and total serum IgE, and by determining PBC in vitro proliferation and cytokine secretion in response to O. volvulus antigen.

Of 691 individuals studied, 219 presented with onchocerciasis-associated skin changes. The groups of individuals with and without skin lesions neither differed in prevalences nor in average numbers of microfilariae. Compared with individuals without skin lesions, pronounced systemic T-helper (Th) 2-type responses were found with a trend of increasing intensity in the order of depigmentation, papular dermatitis, atrophy and lichenified dermatitis. Differences between the groups were most pronounced for serum IgE, less so for eosinophilia, and relatively weak for PBC proliferation and interleukin-5 secretion.

Skin lesions in onchocerciasis are associated with a spectrum of increasing generalized Th2-type responses ranging from low reactivities in cases of depigmentation alone to strong reactivities in cases of lichenification.